Implement typing.cast

test/completion/pep0484_typing.py

@@ -351,3 +351,14 @@ def foo(a: typing.List, b: typing.Dict, c: typing.MutableMapping) -> typing.Type
     c['asdf']
 #? int
 foo()
+
+def cast_tests():
+    x = 3.0
+    y = typing.cast(int, x)
+    #? int()
+    y
+    return typing.cast(str, x)
+
+
+#? str()
+cast_tests()